【Therefore】 , 【hence】 ,  【consequently】 ,  【then】 ,  【accordingly】 ,  【so】  are adverbs used as connectives to indicate logical or causal sequence.

They vary in the degree of closeness of connection suggested as well as in the kind of sequence implied.

【Therefore】  and  【hence】  are employed chiefly to indicate that what follows is a necessary deduction from what has preceded.

【Therefore】 commonly introduces a conclusion.

【Hence】  , though often interchangeable with  【therefore】 , stresses the importance of what precedes.

【Consequently】 , though often used to introduce a deduction, does not always imply necessity in the inference. Rather it suggests good grounds for the conclusion or implies a strong antecedent probability. It also may indicate that what follows is a result of what precedes.

【Then】 , when used to indicate logical sequence, is employed chiefly in the consequent clause or conclusion in a conditional sentence.

【Accordingly】 usually indicates logical or causal sequence but connotes naturalness or usualness in what follows as a consequence rather than necessity or inevitability.

【So】 is typically found in more casual expression and is often indefinite in its suggestion of which kind of sequence is indicated.